How do scientists predict a hurricane's path?

EXPLAIN IT TO ME

Q: How do meteorologists determine the path of a hurricane such as Irene, which appears headed toward the United States?

A: Orbiting satellites scan the storms with visible, infrared and other types of imagery. Closer to Earth, special planes, balloons and other devices are used.

Cameras in satellites allow scientists to determine the size and structure of each storm, helping them determine whether it is becoming stronger or unraveling.

Infrared readings measure among other things the temperature of the storm's cloud tops, helping determine the height of the storm. Such readings also can measure the temperature of the ocean beneath the storm; warm waters provide energy to hurricanes.

Measures taken by balloons and planes flying into or near the storm cover variables such as atmospheric pressure, wind direction and speed, wind sheer, air temperature and humidity. Ground-based Doppler radar joins the effort as the storm moves closer to land.

All the data is fed into computer models designed to predict how the storm will move through the atmosphere. The models forecast the storm's strength and offer best estimates on its direction across water and land.

The National Weather Service issues public advisories and "strike probabilities" based on the computer modeling as much as 72 hours in advance of landfall. Today's technology and modeling software allows for five-day forecasts.

Spokesmen from the Weather Service's Florida-based National Hurricane Center and from the Federal Emergency Management Agency said Tuesday that residents all along the U.S. East Coast should be alert to a potential direct landfall later this week.

Irene, downgraded to a Category 1 storm Tuesday afternoon, was heading over the Turks and Caicos Islands and southeastern Bahamas. It was expected to become a major Category 3 storm, with winds in excess of 111 mph by Wednesday and could possibly intensify further to a Category 4 as it neared the southeast U.S. coast by Friday. Follow Irene's track online at http://www.nhc.noaa.gov. Sources: National Weather Service, New York City Office of Emergency Management.

— Pete Leffler, The Morning Call

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